FISA was a Bush administration program codified in 2008 – which was due to expire on Friday at midnight – that allowed the government to eavesdrop on Americans' phone calls and emails without a warrant, as long as one of the parties was believed to be outside the US.

The measure was approved by the House in September, and the Senate had been debating a handful of amendments that would add oversight and privacy safeguards.

Ultimately, senators refused to enact an amendment which would have extended FISA for only three years (as opposed to five), another which would have required the government to account for how many times communications had been intercepted, and another prohibiting US intelligence agencies from reviewing the communications of those caught in the program, Wired magazine reported.

David Kris, a former top anti-terrorism attorney at the Justice Department, told Wired that the FISA Amendments Act gives the government nearly carte blanche spying powers.

Critics of FISA have said it makes a mockery of the Fourth Amendment, which requires a warrant for any searches. Salon pointed out that the government can now seek "programmatic warrants" which allow them to collect massive amounts of data from broadly defined "targets" over the course of a year, in the name of national security.

"As usual, the Senate’s few civil libertarian-leaning voices (a couple Democrats and sometimes Rand Paul) were repeatedly told that their concerns didn’t matter Because of Terror, and amendments designed to provide some small measure of oversight and disclosure into the NSA’s eavesdropping of Americans failed miserably in late-evening votes yesterday," wrote Salon.